Shale Beds Research Articles

Petrography and Geochemistry of Sandstones of Eocene Kopili Formation, Shillong Plateau: Implications on Paleo-weathering, Provenance and Tectonic Setting

ABSTRACT Geochemical and mineralogical studies were carried out on the sandstones of the Eocene Kopili Formation, Shillong Plateau to evaluate paleo-weathering, provenance and tectonic setting. The study area is located on the bank of the Lubha River along the Badarpur-Jowai road section. The Kopili Formation is represented by a sequence of alternation of shales and sandstones. The sandstone beds are usually thin, fine grained, ferruginous and mostly parallel laminated. The thickness of the sandstone beds increases towards the top with decreasing numbers of shale beds. Petrographically the sandstones are dominated by monocrystalline and polycrystalline quartz followed by feldspar, mica and rock fragments. The matrix content does not exceed 15% and hence the sandstones can be classified as arenite. The Kopili sandstones are classified as quartz arenite to sublitharenite, and arkose to sublitharenite based on their petrographic and geochemical parameters respectively. Arenitic composition and high SiO2/Al2O3 ratio indicate that the Kopili sandstones are highly mature. The weathering indices mostly indicate low to moderate (except 49D sample) degree of chemical weathering under arid to semi humid climatic conditions. The major and trace element-based diagrams and their ratios indicate that the Kopili sandstone received sediments from felsic dominated source with minor contribution from basic source rocks and are deposited in tectonically passive margin setting.

A novel wettability index and mineral content curve based shut-in time optimization approach for multi-fractured horizontal wells in shale gas reservoirs

An appropriate shut-in after fracturing can dramatically enhance performance of wells in shale gas reservoirs. In this study, a novel wettability index and mineral content curve based shut-in time optimization approach was proposed. First, a new experimental device for spontaneous imbibition of fracturing fluid under the conditions of formation temperature and confining pressure was designed. Then, we conduct a set of experiments on shale samples from the Longmaxi Formation (LF) in the Sichuan Basin to measure the water-wet index and determine the critical value of clay content. Finally, the low-field nuclear magnetic resonance (NMR) equipment was used to monitor the water flow in shale micro-pores, based on this, the shut-in time for different shale reservoirs was optimized. The experimental results show that LF shale hydration can induce new micro-fractures, and the fractures shape is mainly shale bedding fractures, with obvious directionality. The clay content is the key factor affecting water wettability of shale and the critical clay content value of type I and type II shale reservoirs was about 39.5%. The optimal shut-in time of type I and type II shale reservoirs are about 20 days and 15 days respectively. Field application of three wells showed that the average daily gas production was increased by 2–3 times. The research results can guide the development of shale gas reservoirs effectively.

Composition of Formation Water and Natural Gas as an Indicator of Shale Gas Preservation Conditions: A Case Study of the Marine Shale of the Niutitang Formation in the Cengong Block in Northern Guizhou, China.

Shale gas (SG) wells in the Wufeng–Longmaxi Formation in northern Guizhou differ considerably in their production capacities. Preservation conditions are a crucial factor affecting the formation of SG reservoirs. In this study, the formation water (FW) in four wells in northern Guizhou was analyzed to determine the type; the Cl/Mg, Ca/Mg, and Na/Cl coefficients (CCl/Mg, CCa/Mg, and CNa/Cl, respectively), and the coefficient of desulfurization (Cd); the SG in these wells was tested to identify its composition and the sources of its components. The results show the following: wells TX1 and CY1 contain two types (CaCl2 and NaHCO3) of FW, each with low CNa/Cl, low Cd, high CCa/Mg, and high CCl/Mg, suggesting a high level of FW retention. The FW in wells TM1 and CD1 is of NaHCO3 type and is characterized by high CNa/Cl, high Cd, low CCa/Mg, and low CCl/Mg, indicating a high level of connectivity between the FW and surface water. Nonhydrocarbon gases account for a high proportion of SG in composition; with a 15N value between −8.7 and −4.2‰, N2 accounts for approximately 20% of SG in wells TX1 and CY1, respectively. This result indicates the ammonification of organic matter (OM) during pyrolysis and hydrocarbon generation as sources of N2. In contrast, with a 15N value between −3.6 and 0‰, N2 accounts for over 70% of SG in wells TM1 and CD1, respectively, indicating the atmosphere, the ammonification of OM, and the presence of poor preservation conditions due to a high level of connectivity between the shale bed and the atmosphere acted as the sources of N2. The metamorphism coefficients of FW in conjunction with the SG composition and the sources of nonhydrocarbon gases can serve as auxiliary indicators of the quality of SG preservation conditions.

Fracturing of shales with slots under uniaxial compression parallel to bedding layers

Shale samples containing single pre-machined slots were tested under uniaxial compression directed along with bedding layers. Observed fractures were initiated by the slots, however, their further development was controlled by the shale bedding layers. Slots normal to the loading direction also cause fracturing and reduce failure load. The fracturing is initiated by tensile stress generated at the slot surface due to convergence of the initial open slot. Therefore, the presence of initial aperture in pre-existing cracks or fractures is capable of changing the mechanism of fracture generation. Three kinds of macroscopic fractures are observed: tensile fractures along bedding layers, shear fractures along the inclined direction, and buckling fractures at the final failure moment. Three types of microcracks are identified: shear microcracks produced from initial weak micro-planes unrelated to the bedding layers, tensile microcracks produced from the shear microcracks in the form of wing cracks, and shear microcracks induced by high uniaxial compression stress. The growth of wing cracks can be assisted by the bedding layers. The research results will contribute to the understanding of failure mechanisms of rocks containing prominent bedding layers.

Mechanical Properties of Lamellar Shale Considering the Effect of Rock Structure and Hydration from Macroscopic and Microscopic Points of View

It is well known that the effect of shale hydration causes wellbore instability due to water phase invasion of drilling fluid to lamellar shale rich formations. This is because of that the mechanical properties (compressive strength, elastic modulus, etc.) of lamellar shale surrounding the borehole, which is rich in clay minerals, will decrease significantly after hydration. In this study, using the lamellar shale in the continental stratum of the southern Ordos Basin, the mechanical properties of lamellar shale were studied by compression tests considering the effect of lamellar structure and hydration from a macroscopic point of view. In addition, the mechanical mechanism was discussed combined with the CT scanning tests results from a microscopic point of view. The results demonstrate the following points. Lamellar shale has stronger anisotropy than bedding shale, the compressive strength (deviatoric stress) and elastic modulus of lamellar shale are both lower than those of bedding shale, and it is more prone to tension fracture. With the increase in the angle (β) between the lamina and the axial direction from 0° to 90°, the compressive strength of lamellar shale decreases when β < 30° and then increases, the elastic modulus of lamellar shale decreases greatly when β < 30° and then tends to flatten. With the increase in hydration time, the compressive strength and elastic modulus of lamellar shale both gradually decrease, and the rates of their decrements reduce. The mechanical properties of lamellar shale are more affected by hydration than those of bedding shale. The hydration of lamellar shale leads to the formation of new fractures and the expansion of existing fractures in the junction area between the laminae and rock matrix, resulting in easy tension fracture along the laminae of shale.

Study on the Evolution Law of Shale Hydraulic Fracture Interacting with Bedding Layer under Pulsation Loading

Abstract The bedding layers in shale reservoirs are highly developed with numerous bedding joints. In the hydraulic fracturing process, the propagation of hydraulic fractures during shale formation significantly affects the efficient development of reservoirs. In this study, we employed the pulsating cyclic loading technique to develop a model of the interaction between shale hydraulic fractures and bedding layer; in addition, we used a numerical model optimization method for the zero-thickness cohesive element to compare the hydraulic fracture and bedding layer propagation behavior under static and pulsating loading. We studied the propagation behavior of pulsating fracturing bedding layers at different frequencies, amplitudes, and bedding angles. The results revealed that static load fracturing is more conducive to the propagation of primary fracture under the same conditions, and that pulsation fracturing is better for the propagation of bedding layer. The higher frequency and amplitude of the seismic source in the pulsation fracturing process are more favorable to crossing the bedding layers. When the bedding angle is approximately 10°, turning the main fracture along the bedding direction is challenging. The hydraulic fracture along bedding layer propagation was achieved when the bedding angle was approximately 30° and 45°. When the bedding angle was approximately 60° or more, the fracture extended only along one side of the bedding layer. The study results provide guidance for the formation of fracture networks in the field of fracturing construction of shale reservoirs, thus improving the production of shale reservoirs.

Effect of formation strength anisotropy on wellbore shear failure in bedding shale

The shale gas/oil is playing an important role in the current energy resources. However, the wellbore instability problems bring a high risk to drilling engineering especially in the formation with bedding planes. A normal wellbore stability analysis approach is based on elasticity, which is not enough to recognize the mechanisms. In this paper, the poroelasticity was adopted to present the hydro-mechanical coupling effect in shale formation, meanwhile, the permeability anisotropy which could affect the effective stresses around the well was considered. A three-dimensional finite difference model was developed to simulate arbitrary directional well in shale by the coordinate transformation method. The jointed material model was proposed to character the strength anisotropy and plastic behavior of bedding shale. Additionally, the effects of well trajectory, bedding plane orientation and mud weight on shale wellbore stability were discussed, thus some implications for improving wellbore stability in bedding shale formation were obtained from the proposed model. • The jointed material model is proposed to analyze the shear failure region in bedding shale. • The poroelastic theory is adopted to represent the hydro-mechanical coupling effect in the formation. • A finite difference three-dimensional model is established to simulate the wellbore failure behavior. • The effects of well trajectory, bedding plane orientation and mud weight on wellbore stability are evaluated.

Paleoenvironment, Diagenesis and Thermal History of the Permian Irati Formation Shale Beds in the Paraná Basin, Brazil: An Integrated Approach Based on Mineralogical and Organic Imprints

Paleoenvironment, Diagenesis and Thermal History of the Permian Irati Formation Shale Beds in the Paraná Basin, Brazil: An Integrated Approach Based on Mineralogical and Organic Imprints

The experimental methods and elastic properties of shale bedding planes materials state-of-the-art review

The identification of physical properties and fracture behavior of shale or hydrocarbon materials has grown to have substantial importance in the last four decades to industry and investigators alike due to its importance in unconventional oil and gas resources. This interest deviates from shale being a transversely isotropic material formed by bedding layers with different orientations and isotropic properties. In this paper, the experimental setup and the mechanical properties of shale materials have been reviewed. The investigator shows that the properties of shale are not unique, and it is highly dependent on, volume, loading type, and geolocation. Furthermore, the investigator utilized different experimental setup methods to identify the elastic properties of shale and the most common methods are Transducers Strain Detection, Strain gauges, Ultrasonic, and Digital image correlation that is shown in detail.

Shallow Marine Cenomanian-Turonian Benthic Foraminifera and Kerogen Type from Mangoule, Logbadjeck Formation, Douala/Kribi-Campo Basin, Cameroon, West Africa

An integrated benthic foraminiferal and organic matter analysis of samples obtained from sedimentary sections exposed in the Mangoule-Bonepoupa area, revealed a very shallow marine paleo-depositional environment for the sediments studied, with considerable influx of continental organic matter that were accumulated during the Cenomanian-Turonian age. With reference to the lithostratigraphic profile of the Douala/Kribi-Campo Basin, the age obtained reveals that the sedimentary sections studied belong particularly to the lower section of the Logbadjeck/Mungo River Formation, based on the following benthic foraminifera assemblage: Ammobaculites jessensis, Ammobaculites benuensis, Ammobaculites coprolithiformis, Ammotium cf nkalagum, Ammotium nwalum, Haplophragmoides cf beuchensis, Trochamina taylorana. A particularly very poor palynomorph assemblage was recovered and included no age diagnostic species: Acrostichum aureum, Lycopodiumsporites sp., Fungal spore, Lavigatosporites discordatus, Longapertites sp., Verrucosisporites sp. An organic petrographic analysis performed on these samples revealed Kerogen Type-II and Type-III. The entire data sets obtained from this area is remarkably poor and we suspect poor preservation as the cause viewing the extent of weathering. The paleo-depositional environment of these sediments was suggested both from the foraminifera and palynomorphs present and confirmed from the organic matter types and macrofossil contents. The studied sections are composed generally of dark to dark-gray shale beds. As one of the petroleum producing basins within the Gulf of Guinea in which exploration/exploitation activities are on-going, the current research is aim at providing more data useful in the continuous search for more potential source rocks in this basin.

Experimental and Numerical Simulation of Interlayer Propagation Path of Vertical Fractures in Shale

The complex fracture network formed by volume fracturing of shale gas reservoir is very important to the effect of reservoir reconstruction. The existence of bedding interface will change the propagation path of the hydraulic fracture in the vertical direction and affect the reservoir reconstruction range in the height direction. The three-point bending test is used to test and study the mechanical parameters and fracture propagation path of natural outcrop shale core. On this basis, a two-dimensional numerical model of hydraulic fracture interlayer propagation is established based on the cohesive element. Considering the fluid-solid coupling in the process of hydraulic fracturing, the vertical propagation path of hydraulic fracture under different reservoir properties and construction parameters is simulated. According to the results, the strength of the bedding interface is the weakest, the crack propagation resistance along the bedding interface is the smallest, and the crack propagation path is straight. When the crack does not propagate along the bedding interface, the fracture propagation resistance is large, and the fracture appears as an arc propagation path or deflection. The difference between vertical stress and minimum horizontal stress difference, interlayer stress difference and interface stiffness will have a significant impact on the propagation path of vertical fractures. Large injection rate and high viscosity fluid injection are helpful for vertical fractures to pass through the bedding interface, and low viscosity fracturing fluid is helpful to open the bedding interface. This research work is helpful to better understand the characteristics of bedding shale and the interlayer propagation law of vertical fractures, and to form the stimulation strategy of shale gas reservoir.

Lithostratigraphy and microfacies analysis of Avanah Formation (Middle Eocene) in Gomaspan section northeast Erbil City, Kurdistan region, Iraq

Lithostratigraphy and microfacies analysis of the Avanah Formation (Middle Eocene) were studied in the Gomaspan section in the Bina Bawi anticline, northeast of Erbil city, Kurdistan Region, Iraq. The field observations refer that the formation attains 56 m of medium to thick bedded yellow limestone, grey dolomitic limestone and blue marly dolomitic limestone interbedded with thin beds of blue marl and dark grey shale with an interval of sandy limestone in the middle part and thin to medium bedded limestone interbedded with red mudstone. The petrographic study of 29 thin sections of Avanah carbonates revealed that the majority of the matrix is carbonate mud (micrite) with few microspar. The skeletal grains include benthic foraminifera, dasycladacean green algae, ostracods, calcispheres, pelecypods, rare planktonic foraminifera and bryozoa in addition to bioclasts. Non-skeletal grains encompass peloids, oncoids, intraclasts and extraclasts with common monocrystalline quartz. Based on the field observation and petrographic analysis, three different lithostratigraphic units were identified. They are in ascending order: A-Thick bedded dolomitic marly limestone interbedded with shale. B- Bedded interbedded with red mudstone. Depending on detailed microfacies analysis of carbonate rocks, three main microfacies and 12 submicrofacies are recognized. From the sum of all petrographic, facies, textural analyses, it is concluded that Avanah Formation in Gomaspan section, was deposited in shallow marine environment, semi restricted lagoon, in lower and upper parts and open lagoon environment in the middle part interval.

Lithostratigraphy and microfacies analysis of Avanah Formation (Middle Eocene) in Gomaspan section northeast Erbil City, Kurdistan region, Iraq

Lithostratigraphy and microfacies analysis of the Avanah Formation (Middle Eocene) were studied in the Gomaspan section in the Bina Bawi anticline, northeast of Erbil city, Kurdistan Region, Iraq. The field observations refer that the formation attains 56 m of medium to thick bedded yellow limestone, grey dolomitic limestone and blue marly dolomitic limestone interbedded with thin beds of blue marl and dark grey shale with an interval of sandy limestone in the middle part and thin to medium bedded limestone interbedded with red mudstone. The petrographic study of 29 thin sections of Avanah carbonates revealed that the majority of the matrix is carbonate mud (micrite) with few microspar. The skeletal grains include benthic foraminifera, dasycladacean green algae, ostracods, calcispheres, pelecypods, rare planktonic foraminifera and bryozoa in addition to bioclasts. Non-skeletal grains encompass peloids, oncoids, intraclasts and extraclasts with common monocrystalline quartz. Based on the field observation and petrographic analysis, three different lithostratigraphic units were identified. They are in ascending order: A-Thick bedded dolomitic marly limestone interbedded with shale. B- Bedded dolomitic limestone interbedded with shale and marl. C- Thin to medium bedded limestone interbedded with red mudstone. Depending on detailed microfacies analysis of carbonate rocks, three main microfacies and 12 submicrofacies are recognized. From the sum of all petrographic, facies, textural analyses, it is concluded that Avanah Formation in Gomaspan section, was deposited in shallow marine environment, semi restricted lagoon, in lower and upper parts and open lagoon environment in the middle part interval.

The Influence of Lamina Density and Occurrence on the Permeability of Lamellar Shale after Hydration

The characteristics of laminae in lamellar shale oil reservoirs have important influences on reservoir parameters, especially permeability. In order to explore the influence of lamina density and occurrence on the permeability of lamellar shale after hydration, we studied the lamellar shale in the Chang 7 member of the Yanchang Formation of Triassic in Ordos Basin. By comparing the permeability of bedding shale and lamellar shale with different densities of laminae, it was found that the permeability anisotropy of lamellar shale was stronger. In the direction parallel to the lamina, the permeability increased approximately linearly with an increase in lamina density. The effect of hydration on rock micropore structure and permeability was studied by soaking shale in different fluids. Most of the microfracture in the lamellar shale was parallel to the lamina direction, and hydration led to a widening of the microfracture, which led to the most obvious increase in permeability parallel to the lamina. Collectively, the research results proved that lamina density, occurrence, and hydration have a significant influence on the permeability anisotropy of lamellar shale.

3D Integrated Structural, Facies and Petrophysical Static Modeling Approach for Complex Sandstone Reservoirs: A Case Study from the Coniacian\u2013Santonian Matulla Formation, July Oilfield, Gulf of Suez, Egypt

The Coniacian–Santonian Matulla Formation is one of the important reservoirs in the July oilfield, Gulf of Suez Basin. However, this formation is characterized by uncertainty due to the complexity of reservoir architecture, various lithologies, lateral facies variations and heterogeneous reservoir quality. These reservoir challenges, in turn, affect the effectiveness of further exploitation of this reservoir along the Gulf of Suez Basin. In this work, we conduct an integrated study using multidisciplinary datasets and techniques to determine the precise structural, petrophysical, and facies characteristics of the Matulla Formation and predict their complex geometry in 3D space. To complete this study, 30 2D seismic sections, five digital well logs, and core samples of 75 ft (ft = 0.3048 m) length were used to build 3D models for the Matulla reservoir. The 3D structural model shows strong lateral variation in thickness of the Matulla Formation with NW–SE, NE–SW and N–S fault directions. According to the 3D facies model, shale beds dominate the Matulla Formation, followed by sandstone, carbonate, and siltstone beds. The petrophysical model demonstrates the Matulla reservoir's ability to store and produce oil; its upper and lower zones have good quality reservoir, whereas its middle zone is a poor quality reservoir. The most promising areas for hydrocarbon accumulation and production via the Matulla reservoir are located in the central, southeast, and southwest sectors of the oilfield. In this approach, we combined multiple datasets and used the most likely parameters calibrated by core measurements to improve the reservoir modeling of the complex Matulla reservoir. In addition, we reduced many of the common uncertainties associated with the static modeling process, which can be applied elsewhere to gain better understanding of a complex reservoir.

Lower Gondwana megaflora, palynoflora, and biomarkers from Jagannath Colliery, Talcher Basin, Odisha, India, and its biostratigraphic significance

The study of megafossils, palynomorphs, and biomarkers has been carried out from a fossiliferous section of Jagannath Colliery, Talcher Basin, Odisha, India. The megafloral assemblage recovered from the carbonaceous shale bed of the investigated section comprises 15Glossopterisspecies (leaf form),Vertebraria indica(root form), and stem cast of the order Glossopteridales. The megafloral assemblage and lithology (grey shale, carbonaceous shale, sandy shale, and coal seams) of the litho‐column suggest that the sediments belong to the Barakar Formation (Artinskian‐Kungurian age). Palynoflora recovered from the section is dominated byStriatopodocarpitesspp. (35–44%) and subdominated byFaunipollenitesspp. (29–35%) along with a good percentage ofDensipollenitesspp. Stratigraphically significant taxa of this palynoassemblage show its affinity toward the late Permian (Wuchiapingian‐Changhsingian) palynoflora which is geologically mapped as Barakar Formation of early Permian (Artinskian‐Kungurian) age. As a result, to clearly delimit the distribution of different lower Gondwana strata in this area, more precise palynological sampling and extensive geological mapping should be undertaken. The dominant occurrence of short‐chainn‐alkanes in the samples suggests the abundance of algal and microbial sources that are deposited in moderate water level conditions in the basin. Pristane/phytane ratio suggests oxic settings while the hopane distribution in the studied samples suggests significant bacterial degradation of the peat biomass in the depositional milieu.

Peridynamic simulation on hydraulic fracture propagation in shale formation

The inhomogeneity of shale reservoirs, bedding properties and in-situ stress make crack propagation paths complex and diverse in hydraulic fracturing. However, the simulations on hydraulic fracture propagation in shale gas reservoirs still require an effective alternative numerical method. In this paper, a peridynamic (PD) fluid–solid coupling model was developed for the numerical simulation on the hydraulic fracturing process in bedding shale formation. Firstly, a modified bond-based peridynamic (BB-PD) theory was formulated by introducing normal bond, tangential bond and pressure bond. This removes the limitation of classical BB-PD theory on Poisson's ratio. Secondly, a fluid–solid coupling model was established by combining the modified BB-PD theory with pressure driven fluid transport in porous medium. Thirdly, a fracturing criterion for the modified BB-PD theory was derived from energy conservation. Fourthly, the PD fluid–solid coupling model was numerically discretized and verified by three-point bending tests on shale beam. Their accuracy was further checked through the Terzaghi's consolidation problem. Finally, numerical simulations were conducted to explore the generation of hydraulic fracturing induced fracture network in bedding shale formation under different dip angles and horizontal stress ratios. The simulation results showed that the horizontal stress ratio has a greater effect on fracturing pressure, and the dip angle plays a crucial role in the shape of fracture network. The increase of horizontal stress ratio leads to the increase of fracturing pressure.

Characterization of shale gas reservoir of Lower Gondwana litho-assemblage at Mohuda sub-basin, Jharia Coalfield, Jharkhand, India

In quest of unconventional energy as shale gas, lower Gondwana shale-heterolith litho-assemblages of Mohuda sub-basin of Jharia Coalfield have been explored to envisage their potentiality for shale gas generation. A comprehensive approach has undertaken through measurement of in-situ gas content, petrography, rock-eval pyrolysis, proximate analysis, TOC, adsorption isotherm, SEM-EDX and XRD of selected drill core samples to establish potential shale horizons in Barren Measure and Barakar Formations. The in-situ gas content varies from 0.15 to 3.69 m 3/t with increasing depth. High palaeo-geothermal gradient in order of 5.57–6.19 °C/100 m is established where emplacement of intrusive played a dominant role. Interrelation of palaeodepth and vitrinite reflectance points to erosion of 2500 m strata in Mohuda sub-basin. Average TOC content of 9 to 17 wt% indicates excellent organic richness of source rock, while other parameters like S1, S2 and PY derived from rock-eval pyrolysis indicate fair to very good/excellent source condition for hydrocarbon generation. HI, OI, S2, TOC, VRo and Tmax values and their inter-relationships reveal Type III and Type IV kerogens coming under gas window zone of mature to post mature stage. Increase in volatile matter and fixed carbon and decrease in moisture content with depth suggest enhanced gas generation and retention capacity. Quartz dominated mineralogy in shale beds account for suitable hydrofracturing process. GIP of about 7.5 BCM of gas has been assessed and categorized depth wise and formation-wise for Raniganj, Barren Measure and Barakar formations. Experimentally calibrated adsorption isotherm data reveals favourable parameters like gas saturation level (GSL), reservoir pressure to be dropped for initiation of production (ΔP), critical desorption pressure for gas yield (PCR) and abandonment pressure (PAB) in respect of potentiality for production with an average gas recovery factor of 94.5% for all three studied shale zones, which strongly recommends the convenient reservoir characteristic for future exploitation.

Coexistence and Development Model of Multi-Minerals Dominated by Multilayer Magma Intrusion

The diversity of coal measure determines the occurrence state and spatial distribution complexity of mineral resources. Abundant resources have become an important part of geological resources and have attracted more and more attention. Coal measure and their overlying and underlying strata often coexist with various mineral resource types, and there is a certain relationship between their genesis and occurrence. In order to further enrich the theory of comprehensive exploration and coordinated development of multi-mineral resources, this paper takes the Huanghebei Coalfield as an example to systematically study the genesis mechanism and occurrence law of coal seam, coalbed methane, and coal-measure shale gas in Late Paleozoic and rich iron ore in Ordovician limestone underlie coal measure. The research is that: 1) The Late Paleozoic Carboniferous-Permian Marine facies, terrestrial facies, and transitional facies all developed in the coal-bearing area in the Huanghebei Coalfield, and the coal seams and mud shales developed well in Shanxi Formation and Taiyuan Formation. 2) Yanshanian magmatic intruded into Ordovician limestone. Contact metasomatism occurred between the ore-bearing hydrothermal fluids and the surrounding rocks, which led to skarn formation. The magnetite mineralization occurred in the metasomatism alteration process, and finally, the contact metasomatic iron deposit was formed; 3) Yanshanian magma intrusion has a significant impact on the generation of coal from coalbed methane and shale gas in the coal measures of Late Paleozoic. The magma carries a lot of heat by baking the coal seam and overlying shale, which is reflected explicitly in the increasing metamorphism degree of coal. Under the action of high temperature, the secondary gas of coal seam and coalbed methane increase sharply. The maturity and thermal evolution of organic matter in shale beds increased, and the shale gas entered a favorable range. The intrusion of magma greatly enhances the thermal evolution of organic matter in coal and shale, forming a variety of coals and promoting the generation and accumulation of coalbed methane and shale gas. At the same time, Mesozoic magmatic intrusion also controlled the formation of rich iron ores. According to the characteristics of mineral development and distribution in the study area, a multi-mineral development and distribution model of “coal - coalbed methane - shale gas - rich iron ore” coexists in the Huanghebei Coalfield, which is referred to as the “Huanghebei model”.

Study on the bedding angle on the mechanical properties of shale

Conventional mechanical tests under static loading can prove that the angle of the shale bedding plane is the main reason for the anisotropy of its mechanical behavior. In order to explore the influence of the angle in the layer on the anisotropic mechanical behavior of shale, the uniaxial compression mechanical tests were carried out under the conditions of 0°, 15°, 30°, 45°, 60°, 75°, and 90°. The results show that (1) the anisotropy degree of shale compressive strength shows the “W” type with the increase in the bedding angle, while the anisotropy degree of elastic modulus and Poisson’s ratio shows the “V” type with the influence of the bedding angle, but the minimum value of elastic modulus is around 45° and the minimum value of Poisson’s ratio is around 30°; and (2) the analysis of variance has a significant effect on compressive strength, elastic modulus, and Poisson’s ratio. Generally speaking, the anisotropic mechanical characteristics of shale have a great influence with the change in the bedding angle. The research conclusion is helpful to understand the mechanical behavior of shale.